In order to calculate the cooling time of plastic injection molded items, it is necessary to acquire the thermal diffusion coefficient of the plastic　resin. Table 1 gives the thermal diffusion coefficients of some major plastic resins.

: The thermal diffusion coefficient of the plastic at the cavity surface temperature (mm2/sec)
　α＝λ／（c・ρ）
　　　λ：Thermal conductivity of the plastic resin(kcal/m• h• °C)
　　　c：Specific heat of the plastic resin(kcal/kg• °C)
　　　ρ：Density of the plastic resin(kg/m3)

Table 1 Thermal diffusion coefficient of major plastic resins